HealthCalc Hub

Due date for a last period in September

Find your due date by month. This page covers a last period in September from day 1 to day 30 and shows where each date lands.

Pick a date to see your due date.

This calculator gives general information only. It is not medical advice. Talk to a doctor or other qualified health professional about your own health.

How it works

The page adds 280 days to your last period start date. That is 40 weeks. In September the due dates run through June and July.

Worked example

Use 15 September as the first day of the last period. Add 280 days for a due date of 22 June. The range for the month is 8 June to 7 July. This example uses a 365-day year.

Estimated due date for each day of September, counting 280 days from the first day of the last period. The table uses a 365-day year.

First day of last periodDue date
1 September8 June
2 September9 June
3 September10 June
4 September11 June
5 September12 June
6 September13 June
7 September14 June
8 September15 June
9 September16 June
10 September17 June
11 September18 June
12 September19 June
13 September20 June
14 September21 June
15 September22 June
16 September23 June
17 September24 June
18 September25 June
19 September26 June
20 September27 June
21 September28 June
22 September29 June
23 September30 June
24 September1 July
25 September2 July
26 September3 July
27 September4 July
28 September5 July
29 September6 July
30 September7 July

Common questions

Does the year change the due date?

Only if the span includes 29 February, which moves the date one day earlier. If the span from 15 September includes a 29 February, 22 June reads one day earlier, as 21 June.

How reliable is a due date worked out by month?

It is an estimate, and births spread across the weeks around it. A last period on day 15 of September gives 22 June, with arrivals spread across the weeks around that date.

Which month will my baby be born?

The due date month is a guide, and many births come earlier or later. A last period in September points to June and July.

What if I only know the month?

Use the middle of the month. The due date then falls in the middle of the window. Day 15 of September maps to 22 June.

How many weeks is the gap?

Divide the days by 7 to get weeks. From day 1 of September to 8 June is 280 days, which is 40 weeks.